Fingerprint scanning method

ABSTRACT

A computer-implemented method entails capturing a digital fingerprint of a finger using a fingerprint-capturing device, collecting pressure measurements using pressure sensors associated with the fingerprint-capturing device as the finger contacts the fingerprint-capturing device, determining a finger-sensor contact direction from the pressure measurements and storing the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/485,060, filed Sep. 12, 2014, and issued as U.S. Pat. No.9,390,308 on Jul. 12, 2016, the entire contents of which areincorporated herein by reference.

TECHNICAL FIELD

The present technology relates generally to biometric authenticationtechniques and, in particular, to fingerprint scanning.

BACKGROUND

Biometric authentication utilizes physical characteristics or traits(biometrics) of the human body to identify the user. One commonly usedtechnique is to capture a digital fingerprint or fingerprint scan and tocompare the digital fingerprint against a previously recorded sample ofthe digital fingerprint. There exist, unfortunately, various techniquesfor defeating a fingerprint authentication system by presenting a copyof the fingerprint image to the scanner. It is thus highly desirable toprovide an improved fingerprint scanning technique.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present technology will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a depiction of a mobile device as one example of a computingdevice which may implement the present technology;

FIG. 2 is a depiction of a mobile device having a fingerprint scannerfor scanning a fingerprint;

FIG. 3 is a flowchart depicting steps, acts or operations of afingerprint scanning method;

FIG. 4 depicts a desktop computer with an externally connectedfingerprint-scanning device;

FIG. 5 is a schematic top view of the fingerprint-scanning deviceshowing an array of force sensors;

FIG. 6 is schematic side view of the fingerprint-scanning device;

FIG. 7 depicts a thumb contacting a fingerprint-scanning device;

FIG. 8 depicts the rolling contact between the thumb and thefingerprint-scanning device;

FIG. 9 depicts a thumb roll in a reverse direction;

FIG. 10 depicts a changing pressure distribution as the thumb rolls ontothe scanner;

FIG. 11 shows a kinematic map of the thumb contacting the scanner;

FIG. 12 shows how particular visual characteristics or artefacts may bevisible in the fingerprint scan at certain forces or pressures; and

FIG. 13 depicts four general roll directions for categorizing userinput.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

The present technology provides a technique for augmenting the securityof a fingerprint scan by also detecting a finger-sensor contactdirection, i.e. a finger-roll direction of a finger as it rolls incontact with an imaging device or scanner.

Accordingly, one aspect of the present technology is acomputer-implemented method that entails steps, acts or operations ofcapturing a digital fingerprint of a finger using afingerprint-capturing device, collecting pressure measurements usingpressure sensors associated with the fingerprint-capturing device as thefinger contacts the fingerprint-capturing device, determining afinger-sensor contact direction from the pressure measurements, andstoring the finger-sensor contact direction in association with thedigital fingerprint for subsequent biometric authentication.

Another aspect of the present technology is a non-transitorycomputer-readable medium comprising instructions in code which whenloaded into a memory and executed by a processor of a computing devicecause the computing device to non-transitory computer-readable mediumcomprising instructions in code which when loaded into a memory andexecuted by a processor of a computing device cause the computing deviceto capture a digital fingerprint of a finger using afingerprint-capturing device, collect pressure measurements usingpressure sensors associated with the fingerprint-capturing device as thefinger contacts the fingerprint-capturing device, determine afinger-sensor contact direction from the pressure measurements, andstore the finger-sensor contact direction in association with thedigital fingerprint for subsequent biometric authentication.

Another aspect of the present technology is a computing devicecomprising a fingerprint-capturing device for capturing a digitalfingerprint of a finger, pressure sensors associated with thefingerprint-capturing device to collect pressure measurements as thefinger contacts the fingerprint-capturing device, wherein the processoris configured to determine a finger-sensor contact direction from thepressure measurements and to cause the memory to store the finger-sensorcontact direction in association with the digital fingerprint forsubsequent biometric authentication. In one implementation, the digitalfingerprint is stored on a smart card external to the device capturingthe digital fingerprint. The fingerprint may then be extracted from thesmart card for matching purposes or, alternatively, the extractedfingerprint (and any associated direction/pressure/speed data) is sentto the smart card to be processed on the smart card which returns apositive or negative identification response without transmitting thefingerprint data from the card.

The details and particulars of these aspects of the technology will nowbe described below, by way of example, with reference to the drawings.

By way of overview, the present technology provides an improved methodfor fingerprint scanning that not only obtains a digital fingerprint butalso detects the direction of the finger as it rolls over thefingerprint scanner or sensor. This method is implemented on a computingdevice 100 that comprises a fingerprint-capturing device 200 forcapturing a digital fingerprint of a finger. The fingerprint-capturingdevice may be any fingerprint imager, reader, scanner or sensor capableof generating an image, model, map, representation or topography of thefinger in sufficient detail to permit comparison with at least one otherpreviously stored fingerprint for the purposes of biometricallyauthenticating a user of the computing device.

The fingerprint-capturing device 200 may be optical, ultrasonic orcapacitance-based.

An optical fingerprint imager captures a digital image of the printusing visible light. The upper layer of the sensor, on which the fingeris placed, is the touch surface under which is a light-emitting phosphorlayer for illuminating the finger. The light reflected from the fingertravels through the phosphor layer to a charge-coupled device whichcaptures the image of the fingerprint.

An ultrasonic sensor employs ultrasonographic techniques to create animage of the fingerprint. The ultrasonic sensor emits very highfrequency sound waves that penetrate the epidermal layer. Piezoelectrictransducers are used to emit and receive the sound waves.

A capacitance-based sensor employs an array of pixels each acting as oneplate of a parallel-plate capacitor, with the electrically conductivedermal layer acting as the other plate, and the non-conductive epidermallayer acting as a dielectric material. The capacitance-based sensor maybe active or passive. An active capacitance sensor uses a charging cycleto apply a voltage to the skin prior to measurement. The electric fieldbetween the finger and the sensor tracks the pattern of ridges in thedermal layer. On the discharge cycle, the voltage potential across thedermal layer and the sensor is measured against a reference voltage tocalculate a capacitance value. The distance values are then calculatedto generate an image of the fingerprint. A passive capacitance sensorgenerates an image of the fingerprint patterns on the dermal layer ofskin. Each sensor pixel is used to measure the capacitance at a givenpoint of the array. The capacitance varies between the ridges andvalleys of the finger.

The computing device used to implement this novel method of scanning afingerprint by also determining a finger-sensor contact direction maycomprise any desktop computer, laptop computer, tablet, notebook, smartphone, personal digital assistant, smart card reader, accessory or thelike. This technology may be applied to kiosks, portable navigationunits, vehicle computer systems, gaming consoles, smart appliances,biometric locks, biometric alarm systems, or any other electronicapparatus, machine, device, system or equipment requiring userauthentication by means of a digital fingerprint.

FIG. 1 is a depiction of a mobile device as one example of a computingdevice on which the present technology may be implemented. This mobiledevice, which is generally designated by reference numeral 100, includesa processor 110 and memory 120, 130 for executing one or moreapplications. The memory may include flash memory 120 and/or randomaccess memory (RAM) 130. Other types or forms of memory may be used.

As depicted by way of example in FIG. 1, the mobile device 100 includesa user interface 140 for interacting with the mobile device and itsapplications. The user interface 140 may include one or moreinput/output devices, such as a display screen 150 (e.g. an LCD or LEDscreen or touch-sensitive display screen), and may optionally include akeyboard or keypad. The user interface may also include an optical jogpad and/or a thumbwheel, trackball, track pad or equivalent.

As depicted by way of example in FIG. 1, the mobile device 100 mayinclude a transceiver 170 for communicating with other devices. Thetransceiver 170 may be a radiofrequency (RF) transceiver for wirelesslycommunicating with one or more base stations over a cellular wirelessnetwork using cellular communication protocols and standards for bothvoice calls and packet data transfer such as GSM, CDMA, GPRS, EDGE,UMTS, LTE, etc.

Where the mobile device 100 is a wireless communications device, thedevice may include a Subscriber Identity Module (SIM) card 112 forGSM-type devices or a Re-Usable Identification Module (RUIM) card forCDMA-type devices. The RF transceiver 170 may include separate voice anddata channels.

Alternatively, where the computing device is a wired device like adesktop computer, laptop, etc., the transceiver 170 of the computingdevice 100 may be a modem or equivalent (for wired communications)using, for example, the TCP/IP protocol for Internet data communication.The mobile device 100 may also include one or more ports for wiredconnections, e.g. USB, HDMI, FireWire (IEEE 1394), etc.

The mobile device 100 optionally includes a speech-recognition subsystemthat has a microphone 180 for transforming voice input in the form ofsound waves into an electrical signal. The electrical signal is thenprocessed by a speech-recognition module (digital signal processor) todetermine keywords or phrases from the voice input. Optionally, themobile device 100 may include a speaker 182 and/or an earphone jack.

The mobile device 100 optionally includes a position-determiningsubsystem such as a global navigation satellite system (GNSS) receiver,for example a Global Positioning System (GPS) receiver 190 (e.g. in theform of a chip or chipset) for receiving GNSS (e.g. GPS) radio signalstransmitted from one or more orbiting GNSS (e.g. GPS) satellites.

Optionally, the mobile device 100 may include a Wi-FiTM transceiver 192,a Bluetooth® transceiver 194, and/or a near-field communications (NFC)chip. The computing device 100 may also optionally include a transceiverfor WiMax™ (IEEE 802.16), a transceiver for ZigBee® (IEEE 802.15.4-2003or other wireless personal area networks), an infrared transceiver or anultra-wideband transceiver.

Optionally, the mobile device may include other sensors like a digitalcompass 196 and/or a tilt sensor or accelerometer 198.

The mobile device 100 of FIG. 1 may implement various forms of biometricaccess control by requiring a user to supply a digital fingerprint. Forexample, device login, login to secure websites or secure applications,banking/financial transactions, etc. may require the user to supply adigital fingerprint for comparison with a previously stored digitalfingerprint. As illustrated by way of example in FIG. 2, the mobiledevice may display a request 202 to provide biometric authenticationinput in the form of a fingerprint scan. The fingerprint scanner 200scans the finger to capture a digital fingerprint. Optionally, thescanning status and fingerprint may be displayed on the display 150 ofthe mobile device 100.

As illustrated in FIG. 3, the method thus entails a step, act oroperation 300 of capturing a digital fingerprint of a finger using afingerprint-capturing device, a step, act or operation 310 of collectingpressure measurements using pressure sensors associated with thefingerprint-capturing device as the finger contacts thefingerprint-capturing device, a step, act or operation 320 ofdetermining a finger-sensor contact direction (i.e. finger-rolldirection) from the pressure measurements, and a step, act or operation330 of storing the finger-sensor contact direction in association withthe digital fingerprint for subsequent biometric authentication.Subsequent biometric authentication involves scanning a fingerprint andcomparing the scanned fingerprint against the stored fingerprint. Anysuitable fingerprint matching algorithm may be employed for thecomparison, e.g. minutiae matching, correlation matching or ridgematching or a combination thereof.

As noted above, the present technology may used by a mobile device(wireless communications device, smart phone, cell phone, tablet,laptop, palmtop, portable navigation device, smart card reader, etc.).The technology may also be used for any other fixed computing device(e.g. desktop personal computer) such as the desktop computer 100depicted by way of example in FIG. 4 which has an externally connectedfingerprint-capturing device 200 (or external accessory device). Theexternal accessory device 200 may also, in other embodiments, beconnected to a mobile device via a wired or wireless connection. It mayoptionally include a tilt sensor or accelerometer to also register thetilt or orientation.

In the embodiment illustrated by way of example in FIGS. 5 and 6, thefingerprint-capturing device 200 includes optical, ultrasonic orcapacitance-based sensors 210 disposed beneath a glass surface orplaten. In addition, the device 200 includes pressure sensors 220 (whichmay be any suitable pressure transducers, force transducers, load cellsor strain gauges, including for example, force-sensing resistors,piezoelectric transducers, etc.). These pressure sensors 220 areassociated with the fingerprint-capturing device to collect pressuremeasurements as the finger contacts the fingerprint-capturing device.These pressure sensors may be embedded or incorporated within the device200.

The processor 110 of the computing device is configured to determine afinger-sensor contact direction from the pressure measurements and tocause the memory to store the finger-sensor contact direction inassociation with the digital fingerprint for subsequent biometricauthentication. In a variant, the device 200 may have its ownmicroprocessor, programmable logic controller, or circuitry to determinethe finger-sensor contact direction. The finger-sensor contact direction(i.e. finger-roll direction) may be represented by a single line orvector or a series of sequential lines or vectors. The finger-sensorcontact direction may be represented by a single curved line or by aseries of sequential curved lines.

In one implementation, the method further entails determining a contactforce for each of the pressure sensors while the finger contacts thefingerprint-capturing device and creating a force profile along thefinger-sensor contact direction (i.e. finger-roll direction). In theexample of FIG. 5, an array or matrix of force values may be created byobtaining a measurement at each force sensor (pressure sensor). Forexample, the force F(1,1) at the sensor in column 1, row 1 is X Newtons,i.e. F(1,1)=x N. A complete matrix of time-varying force values may thusbe determined for F(1,1) to F(N,M) where N is the number of columns andM is the number of rows of sensors. The force profile at each sensor mayalso be time variant as well to provide a more sophisticatedtime-variant force distribution model. The force values are stored witha tolerance or range (delta X) to permit some reasonable degree ofvariation in the force applied by the user during subsequentauthentication.

In one implementation, the method further entails determining a totalcontact time along the finger-sensor contact direction. This contacttime characterizes the speed with which the finger rolls over thefingerprint scanner/sensor. The contact time is another characteristicof the user that can be used to identify the user in addition to thedigital fingerprint. Alternatively, the contact time for each sensor maybe measured. This may be stored with a time tolerance or range (delta).In one embodiment, the delta is greater for the outermost sensors.

In one implementation, in which the fingerprint-capturing device is partof a mobile device as shown in FIG. 1, the method further entailsdetermining a tilt angle of the fingerprint-capturing device using anaccelerometer of the mobile device. In a further variant of thisimplementation, the method further entails measuring variations in tiltwhile the finger contacts the fingerprint-capturing device anddetermining a tilt profile along the finger-sensor contact direction.

The roll direction, time-varying pressure distribution model (forcedistribution model), total contact time and tilt profile may be combinedto generate a highly personalized model of how the user physicallyinteracts with the fingerprint scanner. The mechanics of the contactbetween the user's finger and the sensor thus constitute a personalmotion and force profile that are highly characteristic of the user andare thus useful in biometrically identifying the user. These personalmotion characteristics augment the biometric profile of the user toprovide higher security than a digital fingerprint alone.

Storing various biometric profiles enables a tiered authenticationscheme to control access to various different features, functions orapplications. For example, low sensitivity applications (e.g. access toa social network site) may be made more easily accessible than highsensitivity applications (e.g. an online banking site). In oneimplementation of the method, therefore, the device captures and storesa first finger-sensor contact direction with a first digital fingerprintto define a first biometric authentication profile and captures andstores a second finger-sensor contact direction with a second digitalfingerprint to define a second biometric authentication profile. If theuser authentication matches the first biometric authentication profile,the device grants access to a first set of device functions, e.g. alldevice functions (or any high-security or high-sensitivity function,feature or app). On the other hand, user authentication matching thesecond biometric authentication profile grants access to a second set ofdevice functions, e.g. a subset of the device functions (or anylow-sensitivity applications or features). In another implementation, itis not necessary to explicitly enrol multiple profiles. In this otherimplementation, the user scans a fingerprint multiple times in exactlythe same way to generate N authentication schemes based on {direction,pressure, speed, fingerprint, etc.}, then automatically create thedifferent security profiles by combining groups of them—for example—lowis {fingerprint}, medium is {finger, direction}, high is {all}.

As a variant of this tiered scheme, the device may require only amatching fingerprint scan for access to low-sensitivity applications orfunctions but requires the scan plus the finger-sensor contact directionto access high-sensitivity applications or functions. The user mayconfigure the device to identify those features, functions orapplications for which the augmented biometric authentication profile(fingerprint plus direction) is required.

The embodiments of the present technology exploit the mechanics of thehuman forearm, hand and fingers. It is observed that the bone structureof the human forearm and hand inhibit the thumb (or finger) fromapproaching the sensor in a perfectly horizontal manner. As aconsequence, it is observed from the kinematics of the thumb (or finger)that the thumb (or finger) starts to the make contact around its midsection (as shown in FIG. 7) and, as further pressure is exerted, thetip/end section of the thumb (or finger) then also makes contact. Thekinematics are depicted schematically in FIG. 8. As shown in FIG. 9,even if the sequence (midsection to tip) is reversed (tip tomidsection), a usable, recognizable scan can still be captured. Althougha full pad (with a matrix/array of sensors) is illustrated in FIGS. 5-6,the fingerprint-capturing sensor may be a thin bar having only one rowof sensors instead of a matrix of sensors. In another variant, thesensor plate may have a single row of sensors that are wider to spansubstantially the entire scanner. In other embodiments, thepressure-sensing elements in the array of the scanner may be used tocontrol a pointer on the screen and to receive user input (a userselection analogous to pressing a track pad).

The kinematics and/or dynamics of the finger roll (particularlydirection and speed and force distribution) can be measured as the userscans his or her finger. These kinematic or dynamic values may beassociated with the fingerprint scan to provide an augmented biometricprofile. In one embodiment, the device builds a kinematic model of thefinger roll (direction and speed) by detecting the direction of fingerroll or thumb roll. In another embodiment, the kinematic model isaugmented to become a dynamic model by further measuring forcedistribution (or pressure distribution) as the finger contacts thescanner. The sensors registering the highest forces (loads) may be usedto plot the direction of the thumb roll. FIG. 10 shows by way of examplea pressure distribution as the thumb rolls onto the scanner. FIG. 11shows a kinematic (motion) map of the thumb contacting the scanner. FIG.12 shows how particular visual characteristics or artefacts may bevisible in the fingerprint scan at certain forces or pressures. Theseartefacts may also be characteristic of the user.

In the case of the roll direction, the directional precision required toadequately mimic the roll direction may be reconfigurable or adjustable.For example, the input roll direction may need to be within apredetermined angular threshold of the sample roll direction for thedevice to declare the roll direction to be an adequate match. Thisangular threshold may be adjusted, either manually or automaticallybased on monitoring prior input, to permit some reasonable variations inroll direction. In another implementation, the device may generallycategorize the directions as follows: (1) roll top to bottom, (2) rollbottom to top, (3) roll left to right, (4) roll right to left, (5) swipeup and (6) swipe down. Simplified directions are depicted by way ofexample in FIG. 13.

In another implementation, each of the ten fingers of the user may bescanned. An access code may thus require a user-defined sequence ofscans of different fingers. For example, the user may configure thedevice to request a sequence of scans such as left forefinger (i.e. leftindex finger), right thumb, left thumb, right ring finger, left pinkyfinger. To further complicate the authentication process, the rolldirection for each scan may be specified. For example, left index finger(roll right), right thumb (roll up), left thumb (roll down), right ringfinger (roll left), left pinky finger (roll right). Authentication thusdepends not only on the fingerprint scans matching their respectiveexemplars (previously saved fingerprints) but also on the correctsequence of scans and correct roll direction for each finger.

A collateral benefit of the finger rolling over the fingerprint scanneris that the scanner can detect more of the fingerprint than if thefinger were to be pressed flat against the scanner. For example, if thefinger is rolled from left to right, part of the fingerprints on eachside of the finger can be scanned. Similarly, if the finger rolls frombottom to top, it is possible to collect much more of the fingerprintfrom the bottom portion of the finger. By collecting and using thisextra fingerprint information, it is more difficult for an attacker whohas lifted a fingerprint from a glass or other object because a liftedfingerprint typically would only include the smaller flat portion of thefingerprint. Since the fingerprint roll includes a larger image thatincludes the peripheral contours of the fingerprint (i.e. sides andforward tip portion), an attacker would be hard pressed to reproduceenough of the fingerprint to make an attack successful.

The amount (i.e. total surface area) of fingerprint scanned may be alsobe used to determine the security profile that is used by the device. Inother words, if the scan includes the peripheral contours (sides and/ortip portion of the finger in addition to the underside of the finger)this greater surface area of scan may be used by the device to grant ahigher level of access than a scan of smaller area, e.g. a scan limitedto only the underside of the finger. To implement this, the processor isconfigured to compare a total surface area of the scanned fingerprint toa predetermined threshold, to grant access to a first set ofapplications if the threshold is met or exceeded and to grant access toa second set of applications if the threshold is not exceeded. Forexample, if the user is attempting to access a low-security applicationand scans a fingerprint in such a way as to only capture part of thefingerprint, e.g. the underside only, access would still be allowedwithout requesting the user to re-scan the fingerprint since what wasscanned is considered to be sufficient for the application needed. Ifthe security of the application is considered to be high, the device mayask the user to re-scan the fingerprint. The device may display anotification to the user that limited access is being granted in view ofthe limited size of the scanned fingerprint. Alternatively, the devicemay display a notification asking the user whether he or she wishes tore-scan the fingerprint in order to gain greater access to thehigher-security applications or functions of the device.

In addition to the fingerprint scan and finger-sensor contact direction,the device may also rely on other concurrent authentication input toprovide multi-factor authentication of the user. This further input maybe in the form of a username and/or password, smart card PIN,cryptographic token, personal verification question(s), voiceprint,facial recognition, retina scan or other environmental data such as thecurrent position of the device.

For the purposes of this specification, it is to be understood thatreferences to “finger” include the thumb. Likewise, references to“thumb” shall be understood as being applicable to a finger. Similarly,the expression “fingerprint” is meant to include a thumbprint.

Any of the methods disclosed herein may be implemented in hardware,software, firmware or any combination thereof. Where implemented assoftware, the method steps, acts or operations may be programmed orcoded as computer-readable instructions and recorded electronically,magnetically or optically on a fixed, permanent, non-volatile ornon-transitory computer-readable medium, computer-readable memory,machine-readable memory or computer program product. In other words, thecomputer-readable memory or computer-readable medium comprisesinstructions in code which when loaded into a memory and executed on aprocessor of a computing device cause the computing device to performone or more of the foregoing method(s).

A computer-readable medium can be any means that contain, store,communicate, propagate or transport the program for use by or inconnection with the instruction execution system, apparatus or device.The computer-readable medium may be electronic, magnetic, optical,electromagnetic, infrared or any semiconductor system or device. Forexample, computer executable code to perform the methods disclosedherein may be tangibly recorded on a computer-readable medium including,but not limited to, a floppy-disk, a CD-ROM, a DVD, RAM, ROM, EPROM,Flash Memory or any suitable memory card, etc. The method may also beimplemented in hardware. A hardware implementation might employ discretelogic circuits having logic gates for implementing logic functions ondata signals, an application-specific integrated circuit (ASIC) havingappropriate combinational logic gates, a programmable gate array (PGA),a field programmable gate array (FPGA), etc.

This invention has been described in terms of specific embodiments,implementations and configurations which are intended to be exemplaryonly. Persons of ordinary skill in the art will appreciate, having readthis disclosure, that many obvious variations, modifications andrefinements may be made without departing from the inventive concept(s)presented herein. The scope of the exclusive right sought by theApplicant(s) is therefore intended to be limited solely by the appendedclaims.

1. A computer-implemented method comprising: capturing a digital fingerprint of a finger using a fingerprint-capturing device; collecting pressure measurements using pressure sensors associated with the fingerprint-capturing device as the finger contacts the fingerprint-capturing device; determining a finger-sensor contact direction from the pressure measurements; determining a contact force for each of the pressure sensors while the finger contacts the fingerprint-capturing device and creating a force profile along the finger-sensor contact direction; and storing the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication.
 2. The method as claimed in claim 1 further comprising determining a total contact time along the finger-sensor contact direction.
 3. The method as claimed in claim 2 wherein the fingerprint-capturing device is part of a mobile device and wherein the method further comprises determining a tilt angle of the fingerprint-capturing device using an accelerometer of the mobile device.
 4. The method as claimed in claim 3 further comprising measuring variations in tilt while the finger contacts the fingerprint-capturing device and determining a tilt profile along the finger-sensor contact direction.
 5. A computer-implemented method comprising: capturing a digital fingerprint of a finger using a fingerprint-capturing device; collecting pressure measurements using pressure sensors associated with the fingerprint-capturing device as the finger contacts the fingerprint-capturing device; determining a finger-sensor contact direction from the pressure measurements; and storing a first finger-sensor contact direction with a first digital fingerprint to define a first biometric authentication profile and storing a second finger-sensor contact direction with a second digital fingerprint to define a second biometric authentication profile, wherein user authentication matching the first biometric authentication profile grants access to a first set of device functions whereas user authentication matching the second biometric authentication profile grants access to a second set of device functions.
 6. A non-transitory computer-readable medium comprising instructions in code which when loaded into a memory and executed by a processor of a computing device cause the computing device to: capture a digital fingerprint of a finger using a fingerprint-capturing device; collect pressure measurements using pressure sensors associated with the fingerprint-capturing device as the finger contacts the fingerprint-capturing device; determine a finger-sensor contact direction from the pressure measurements; determine a contact force for each of the pressure sensors while the finger contacts the fingerprint-capturing device and create a force profile along the finger-sensor contact direction; and store the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication.
 7. The computer-readable medium as claimed in claim 6 further comprising code that causes the device to determine a contact force for each of the pressure sensors while the finger contacts the fingerprint-capturing device and to create a force profile along the finger-sensor contact direction.
 8. The computer-readable medium as claimed in claim 7 further comprising code that causes the device to determine a total contact time along the finger-sensor contact direction.
 9. The computer-readable medium as claimed in claim 8 wherein the computing device is a mobile device and wherein the computer-readable medium further comprises code that causes the device to determine a tilt angle of the fingerprint-capturing device using an accelerometer of the mobile device.
 10. The computer-readable medium as claimed in claim 9 further comprising code to cause the device to measure variations in tilt while the finger contacts the fingerprint-capturing device and to determine a tilt profile along the finger-sensor contact direction.
 11. A non-transitory computer-readable medium comprising instructions in code which when loaded into a memory and executed by a processor of a computing device cause the computing device to: capture a digital fingerprint of a finger using a fingerprint-capturing device; collect pressure measurements using pressure sensors associated with the fingerprint-capturing device as the finger contacts the fingerprint-capturing device; determine a finger-sensor contact direction from the pressure measurements; and store a first finger-sensor contact direction with a first digital fingerprint to define a first biometric authentication profile and store a second finger-sensor contact direction with a second digital fingerprint to define a second biometric authentication profile, wherein user authentication matching the first biometric authentication profile grants access to a first set of device functions whereas user authentication matching the second biometric authentication profile grants access to a second set of device functions.
 12. A computing device comprising: a processor; a fingerprint-capturing device for capturing a digital fingerprint of a finger; pressure sensors associated with the fingerprint-capturing device to collect pressure measurements as the finger contacts the fingerprint-capturing device; wherein the processor is configured to determine a finger-sensor contact direction from the pressure measurements and to cause a memory to store the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication, and wherein the processor cooperates with the pressure sensors to determine a contact force for each of the pressure sensors while the finger contacts the fingerprint-capturing device and to create a force profile along the finger-sensor contact direction.
 13. The device as claimed in claim 12 wherein the processor cooperates with the pressure sensors to determine a total contact time along the finger-sensor contact direction.
 14. The device as claimed in claim 13 further comprising an accelerometer to determine a tilt angle of the fingerprint-capturing device.
 15. The device as claimed in claim 14 wherein the processor cooperates with the accelerometer to measure variations in tilt while the finger contacts the fingerprint-capturing device and to determine a tilt profile along the finger-sensor contact direction.
 16. A computing device comprising: a processor; a fingerprint-capturing device for capturing a digital fingerprint of a finger; pressure sensors associated with the fingerprint-capturing device to collect pressure measurements as the finger contacts the fingerprint-capturing device; wherein the processor is configured to determine a finger-sensor contact direction from the pressure measurements, and wherein the processor cooperates with a memory to store a first finger-sensor contact direction with a first digital fingerprint to define a first biometric authentication profile and to store a second finger-sensor contact direction with a second digital fingerprint to define a second biometric authentication profile, wherein user authentication matching the first biometric authentication profile grants access to a first set of device functions whereas user authentication matching the second biometric authentication profile grants access to a second set of device functions.
 17. The device as claimed in claim 16 wherein the processor cooperates with the pressure sensors to determine a contact time for each sensor.
 18. A computing device comprising: a processor; a fingerprint-capturing device for capturing a digital fingerprint of a finger; pressure sensors associated with the fingerprint-capturing device to collect pressure measurements as the finger contacts the fingerprint-capturing device; wherein the processor is configured to: determine a finger-sensor contact direction from the pressure measurements; and to cause a memory to store the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication; compare a total surface area of the scanned fingerprint to a threshold; grant access to a first set of applications if the threshold is met or exceeded; and grant access to a second set of applications if the threshold is not exceeded.
 19. A non-transitory computer-readable medium comprising instructions in code which when loaded into a memory and executed by a processor of a computing device cause the computing device to: capture a digital fingerprint of a finger on a fingerprint-capturing device; collect pressure measurements as the finger contacts the fingerprint-capturing device using pressure sensors associated with the fingerprint-capturing device; determine a finger-sensor contact direction from the pressure measurements and cause the memory to store the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication; compare a total surface area of the scanned fingerprint to a threshold; grant access to a first set of applications if the threshold is met or exceeded; and grant access to a second set of applications if the threshold is not exceeded.
 20. A method at a computing device, the method comprising: capturing a digital fingerprint of a finger using a fingerprint-capturing device; collecting pressure measurements as the finger contacts the fingerprint-capturing device using pressure sensors associated with the fingerprint-capturing device; determining a finger-sensor contact direction from the pressure measurements; storing the finger-sensor contact direction in association with the digital fingerprint for subsequent biometric authentication; comparing a total surface area of the scanned fingerprint to a threshold; granting access to a first set of applications if the threshold is met or exceeded; and granting access to a second set of applications if the threshold is not exceeded. 